1. Field of the Invention
The present invention relates to a waveform equalizer which equalizes the waveform of a data signal containing waveform distortions.
2. Description of the Related Art
For example, in a hard disk drive, a data signal read from a read head contains waveform distortions, more or less. Accordingly, without giving any processing to the data signal containing waveform distortions, it would be impossible to exactly read data recorded in a hard disk. In a typical hard disk drive, a data signal read from a read head is first amplified by an amplification circuit, and then the waveform thereof is equalized by a waveform equalizer. Then the waveform-equalized signal is fed to a peak value detection circuit, and thus the reading of recorded data is carried out.
Conventionally, a typical waveform equalizer includes a plurality of sample and hold circuits (each referred to as a S/H circuit) connected in a cascade connection, a circuit for weighting outputs of a predetermined number of S/H circuits among the plurality of S/H circuits, and a circuit for effecting an addition of outputs of the weighting circuit to thereby output a waveform-equalized signal. In this constitution, each of the S/H circuits responds to a sampling signal to thereby alternatively repeat a sampling operation and a hold operation. Also, the S/H circuit provided at the first stage receives an input data signal which is the object of waveform equalization.
According to the constitution, however, a problem occurs in that respective sampling errors and hold errors are accumulated, and thus it is impossible to obtain a waveform-equalized output signal with high precision. This is because the input data signal is shifted with being sampled and held in sequence through the plurality of S/H circuits.
Also, since the outputs of the predetermined number of S/H circuits, which alternatively repeat the sampling operation and the hold operation, are fed to the weighting circuit, another problem occurs in that the operation speed is relatively lowered.
Note, the problems in the prior art will be explained later in detail in contrast with the preferred embodiments of the present invention.